GALAXIES

spiral, swirl, cigar galaxy-2401967.jpg

The universe contains billions galaxies. The galaxy includes many stars smaller than our Sun as well as many others that are thousands of times bigger than the Sun. It also includes many other celestial bodies such as clusters of stars, nebulae, clouds of gases, clouds of dust, dead stars, newly born stars, etc. galaxies vary in size, luminosity, and mas.

Many galaxy name begin with the letter M followed by the number. This naming system began when French astronomer Charles joseph (1730-1817) cataloged Steller bodies and gave the numbers in the sequence following as M for his name. Galaxies have a common name also. Example, M31 is also known as the Andromeda galaxy.

A small galaxy can have a diameter of a few thousand light years and contain billions of stars. A large galaxy contain can have a diameter of half a million light-years ( The distance that light can travelled in one year i.e.365 days is measured in light year) and contain more than a trillion stars. Medium size galaxies contain 100-400 billion stars.

The shapes of galaxies:-   Galaxies are classified according to their shape.

a) Spiral galaxy   b) Elliptical galaxies   c) Irregular galaxies     d) A Barred spiral

THE MILKY WAY (Mandakini)

If we observe the clear sky on a dark night, we will see a smoky white band full of stars spreading north-south in the sky. This is the Milky Way. It is also known as ‘Mandakini’. The Milky Way is a part of the ‘Local Group’ of galaxies.  “Local group” contains Andromeda and M33 galaxies and other 35 small galaxies. The “local” term is used because neighbors in the local group are millions of light years from Milky Way. The galaxy that is closest to our Milky Way is called Andromeda. The Milky Way galaxy is spiral galaxy and its diameter is 100,000 light-year. Our galaxy is medium size galaxy and it contains 100-400 billion stars.

The Milky Way is the galaxy in which our solar system is located. Our solar system resides in an arm of the Milky Way. Our solar system revolves around the center of Milky Way every 250 million years.

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